Theodolite



June 2, 1953 cs. GEIER 2,640,267

THEODOLITE Filed June 50, 1949 2 Sheets-Sheet 1 LII H Z d 6 Fig. I

INVENTOR.

' GEORGE GEIER ATTORNEY Patented June 2, 1953 THEODOLITE George Geier, Ridgefield, N. J assignor to Keufiel & Esser Company, Hoboken, N. J., a corporation of New Jersey Application June 30, 1349, Serial No. 102,299

9 Claims.

This invention relates to surveying instruments or theodolites. In certain instruments of this general class which are usually optical reading it has been found advantageous to make the scales, protractors or circles of glass provided with radial graduation lines and numerals either by etching or other means. These glass circles are usually made in the form of an annular glass ring having an accurately ground inside diameter. Other vitreous transparent materials such as Pyrex or quartz may be used for these circles. In the instruments provided with such glass circles, it has always been a problem to satisfactorily mount the glass circle to the metal parts of the instrument.

Inasmuch as glass or quartz has a different coefficient of expansion than any of the metals normally used in surveying instruments, temperature changes such as may be encountered in the ordinary use of the instruments which may range from arctic to tropical temperatures will introduce errors or in extreme cases may even break the vitreous transparent circle if the circle is not properly mounted. For example, if as is usually the case the circle is mounted by fitting its accurately ground inside diameter over an outside diameter of a metal mount, increasing temperature will cause the mount to expand more rapidly than the glass and strain the glass and decreasing temperature will cause the mount to contract more rapidly than the glass so that the circle will become loose on the mount permitting it to shift to a position eccentric to the vertical axis of the instrument and thereby introducing eccentricity errors in the readings taken with the instrument. The invention is useful in any instrument where a protractor member or scale is mounted for rotation on parts which have a substantially diflerent coefficient of expansion than the protractor member.

The object of this invention is to provide means for mounting glass circles in theodolites and like instruments which will not strain the circle or allow it to become loose because of temperature. changes.

The object and the means by which it is obtained will be more fully understood from the following description taken in connection with the accompanying drawings which are more or less diagrammatic and in which:

Figure I is a view in elevation and partly in section showing a theodolite including one embodiment of the novel circle holding means.

Figure II is a view in diagrammatic sectional elevation showing a second embodiment of the novel circle holding means.

Figure III is a view in diagrammatic sectional elevation showing a third embodiment of the novel circle holding means.

The invention seeks to compensate the effect of temperature changes on a protractor member mounted on a rotatable member having a different coefficient of expansion by causing the protractor member to be moved in the axial direction (vertical in the figures) with respect to the mounting member so that the protractor member will contact and be held at different positions on an inclined surface to compensate for the different expansions of the protractor member and the other member in the radial direction.

Referring to Figure I, the theodolite shown has an alidade I mounted for rotation about the vertical axis of the inner center or spindle 34. The alidade I includes standards 3 and 5 and a telescope I. The telescope 1 has a horizontal axle 9 which mounts it for rotation about a horizontal axis. The usual optical means are provided for reading the glass circle 2. A pivoted reflector l5 directs light through the opening I! to the reflector I9 which directs the light downward through the transparent protractor scale 2 to a reversing prism 2i. The reversing prism 2| directs the light .upward through the hollow standard 5, whence it is directed through the hollow axle 9 and through the auxiliary eyepiece 23, the reading of the protractor scale 2 being obtained through the eyepiece 23.

The glass circle 2 is carried by mount 4 having the same coefficient of expansion as the glass which for example may be a suitable iron nickel alloy. Iron nickel alloys decrease in coefficient of expansion with increasing nickel content until the composition known as Invar is reached. With greater proportions of nickel the coefficient of expansion again decreases. In this range of nickel content an alloy having the same coefficient of expansion as any of the commercial glasses may be found. Other minor alloying constituents may be added to these iron nickel alloys. The coefficient of expansion of quartz may also be matched with an alloy of this type surficiently close for practical purposes. The parts 2 and 4 will be considered to make up a protractor member which has a substantially uniform coefiicient of expansion. The cylindrical surface l3 of the mount 4 is accurately machined to fit the inside diameter of the glass circle 2. Since the mount 4 is chosen to have the same coefiicient of expansion as the glass circle 2 they will fit together at all temperatures. A circular The bottom surface of the protractor member comprising the glass circle 2 and the mount: 4

rests on the supporting member 8 which is mounted on the outer center i2forrotationabout the middle center or main bearing t4; A'holding' member to is provided with an inclined surface, the conical surface 6, which engages matching: surface on the mount 4. It is not necessary that both the holding member ID and protractor member be provided with inclined surfaces. For example one or the other'ofi these members may be provided with a: conical: surface which engages a circular edge on theother'm'emher; Surf-acesof revolution'other. thania conemay be useful in certain'embodimentsz However it is not essential that theiinclined' surface oea complete 'surface'oi revolution. For example three or more piano inclined: surfaces: spaced." within theprotractor maybe used;- The spacedsurfaces need not be plano and may be'ofi negligible wid-th approaching a lineor an? edge formed by two other intersecting surfaces. The holding member is internallythreaded to engagean: externally threaded sleeve on the supportingsmemhert. By use of these threads, the spacing of the conical surface s and the surface" of the-supporting member 8? is adjusted at the temperatureiat' which these parts are assembled to'- hold the. protractor member including the mount it and?) the glass circle 2' positively and without strain. Once-this spacing has ibeen adjusted the members" 8 and" [0: may be locked" together as' for example by" inserting a pin radially through thelmembers.

A circular spring: I'sl secured to the holding member'lo holds thezglass'circle Zionthemount 4-;

The: glass circle 2911161111174; supporting member 8- and holding member HI beingr assembled" as' described are placedi oir-theannular projection of:the:outer-center12i Centering screws 1 ii pref erably4= in number: are provided, for moving the supportingv member 85 radially initwog mutually perpendicular directions 'with respecttotheouter center '22.. The'centering screws le. aretused'to adjust the supporting member 8- to. such a. posi-- times will maketthe center-of t-heradiah gradua'-- tion lines. provided on: therglass circle 2 f all on the axisof the cylindrical bearing; surface of the.

outercenter liwhichis inaccurateabearing contact with an" outer: cylindrical surface of the" middle 4 center or main bearing M; This: adjustment is known in the art'as centering and various meansare known fOI'J accomplishingit withgreat accuracy; When thecenteringoperation is completed the holding member flinay be secured to-the outer center 12- by rother screws not in the plane of thesection. The-outer. center l2- a lsoe makesthrustbear-ing contact. with an .upper surface of. a .fiangeprovidedon the .middle, center Hi. The Y centering screws. may, be. eliminated. in certain embodimentswherein the parts. are. made with. sufiicient. accuracy so that the centering of :the circle isaccomplished With-the required. accuracy merely by putting, the partstogether.

The middle-center or. main bearing! is formed very. accurately. sothatit's inner and outer bear.-

ing surfaces are truly concentric. The inner center or spindle 3:; fits accurately within the main hearing i l and is attached to the alidade as by the screws 38. Thus the spindle 34 by making bearing contact with the main bearing 14 assures that the alidade i will be turned about the same axis about which the outer center I?! carrying the glassecircle-t'may be turned? due to the concentricity of the inner and outerbearing surfaces of the main bearing [4.

It is an advantage to use bronze or similar metals for forming the centers of a surveying instrument because they may be easily formed or machined and-have'good bearing properties especially' if"al1oys having some difference in hardness are" used inbearing contact with each other. However steel-or. other metals may also be used. In any event the parts 36, i l, 12, 8 and it should be made of materials having substantially the same coeflicient of expansion so that no relative movement or'strainin-g of" the parts occurs: as a resultof temperattire-changesa The coefiicicnt-of expansion ofsthe'se parts= will be greater than that of: the glass circle 2.

The base plate M is held between the main hearing M andthe projection- 22; The main bearing ld extends downward. to. an externallythreaded sleevean'd the proj cotton 2 2' is internally threaded so that these parts-may be secured together to hold the baserplate It as shown. The projection 22 may be inserted: in a-universal tribach or'levelling head not shown. by means of which the instrument mayberlevelled on a tripod. lt is-tofc'ourse alsopossibie to'make the levelling;

head a permanent part of the instrument.

Anvannular: support '35 is secured .to the. fiat plate: 25 and may be integral therewith: as shown- Thesupport: 35: holds a clamp ring '36- which may be of form well known in :theart and by -means ofwhich the alidade i may be clampedto. the base of the instrument. A- tangent screw not shown may be used in conventional manner with the clamp andz'clainp ring 35 to permit a fine adjustment: of the ali'dad'e; A circular. spring 20 may be attached to theouter center l2. A- pin. clamp- DO'ISAShO W-ZT may: thenhe provided on the ailid'ade' which clampsthe spring. 2G and thereby the outer: center: carrying the glass circle 2 to the'alid'ade' i and causes it to be turned therewith: The pln clamp-operates to force a pina ga'in'st the spring: 28: bending: it slightly and causing itto. come in'contactwith a friction surface. The: invention. is applicable to othercenter system's using other clamping. and setting devices.

Certain of: the important dimensions of the;

embodimentofl ig; Iare-indicated on the draw-- ing; G'ne of'these-is the mean diameter D of the conical eng'agingsurfaces 6. If other forms of inclined surfaces are used the diameter D of an iznaginary circle passing through the center of each contact area' should be used. Other im-- portant" dimensions are the angle 0 which" the inclined surface. 6' makes with the vertical axis, and the vertical or axial distance dfrom-the lower surface of the: protractor member, i. e.; of

the holding member 5* where it makesrcontact with the supporting member S'to the height at which the. conical engaging surfaces have their mean diameter. edge contacts 9i conical: surface; the distance d should be measured to theicircularedge; In the case where two conical-surfaces are in engagement an imaginary circle havinga diameterwl'iich is the mean of the largest and sma llestdia-metersa In the: case where a circular of the engaging surfaces is taken as a basis of measurement.

It can be readily proved that if the equation:

D tan is satisfied, the amount by which the axial (vertical) expansion of the holding member I0 exceeds that of the protractor member (in this case the mount 4) will be just enough to compensate the amount by which the diametrical (horizontal) expansion of the holding member exceeds that of the protractor member or mount (I.

If the value of 0 is chosen conveniently as 45, the axial distance 11 must equal one half the diameter D. The reason for building up the protractor member from the glass circle mount 2 and the iron nickel mount 4 is now apparent. It is possible to make the protractor member completely of glass provided its thickness is great enough with respect to its inside diameter to permit the equation D tan to be substantially satisfied. However it is not usually desirable to make the glass circle from such a heavy piece of glass since in most embodiments it must be of good enough optical quality to permit the transmission of image forming rays. The thickness of the protractor member can be held to a minimum by reducing the diameter D.

Referring next to Fig. II a spindle I02 is provided which is suitable for supporting the alidade of a surveying instrument for rotation. The spindle I02 is accurately fitted to the inner bearing surface of the middle center or main bearing I04. The main bearing I04 is provided with a concentric outer bearing surface about which the outer center I06 may rotate. The outer center I06 is provided with inclined surfaces or a conical surface I08.

The protractor member or glass circle I I0 rests on the supporting member II2 which fits over the outer center I06 but may slide in the axial (vertical) direction with respect thereto. The supporting member I I2 is pushed upward by the resilient member I I0 (which may be a metal bellows or spring) so that its inner diameter is held in contact with the conical surface I08. The resilient member I I4 is backed by an annular member II6 threaded on the outer center I06. Other clamps, etc., may be added to this embodiment as required. A tension member may be used instead of a compression member for the resilient member I I4 to hold the circle I I0 in contact with the surface I08. In the construction shown the parts I06, H2 and H6 may be of bronze or the like or of any other bearing metals which may be used in surveying instruments.

In the embodiment of Fig. II it is not necessary that the dimensions conform to any equation such as the equation given in connection with Fig. I since a spring or other resilient member keeps the protractor member in contact with the conical surface 8 for all temperatures. However the member II2 should fit the member I08 well enough so that it cannot tilt thereon but may move in the axial direction only.

In Fig. III, the main bearing 204 is provided with concentric internal and external bearing surfaces. The spindle 202 fits the inner bearing surface accurately and is intended to support the alidade of atheodolite. The outer center 206 fits 6. the outer bearing surface of the main bearing 204. The protractor member is made up of the glass circle 2 I0 and the mount 2| I which is made of material having the same coefficient of expansion. The protractor member rests on the supporting member 2I2 which in turn rests on a flange provided on the outer center 206. Centering screws 2I8 may be provided which act between the supporting member 2 I2 and the outer center 206 for centering the glass circle 2I0.

'TWO sleeves 2M and H6 positioned one within the other as shown serve to hold the protractor member on the supporting member 2I2. The outer center 206, the supporting member 2 I2 and the holding member or sleeve 2I4 are of the same material or of materials having the same coefficient of expansion. These parts may for ex-- ample be of bronze or the like which has good bearing properties, which is readily formed and is commonly used for the centers of surveying instruments and which has a higher coefficient of expansion than glass. The holding member 2M is accurately fitted within the supporting member 2I2 but it is possible for the sleeve 2 I4 to slide with respect to the supporting member 2I2 in the axial direction. Since the two parts have the same coefficient of expansion, they will remain accurately fitted at all temperatures The sleeve or tie member H6 is provided with an annular flange at its upper end which engages the sleeve orholding member 2M. The tie member 2I6 is secured on its lower end to the outer center 206. Thus. the tie member 2I6 holds the holding member 2 I I so that its conical outer surface engages the conical inner surface of the mount 2H. The tie member 2I6 is made of a material having a higher coefficient of expansion than either the holding member 2 I2 or the protractor member. Sufiicient radial clearance should be provided between the sleeves 2M and 2I6 to allow for differences in radial expansion of these two parts due to the fact that they are made of diiferent materials. A suitable material for the tie member 2I6 is zinc if the aforementioned parts are of bronze. Therefore during temperature changes a differential expansion takes place between the supporting member H2 and the tie member 2I6 as well as between the mount 2 I I and the tie member 2 I 6. Consequently the axial movement between the engaging conical surfaces of members 2 I4 and 2 II is greater than would result from an embodiment constructed according to Fig. I and having a protractor member of the same eifective thickness d.

It can be readily shown that the dimensions D, d, di, and 0 should satisfy the following equation for perfect compensation at all temperatures:

tan 6:

where CB=coefficient of expansion of supporting member 212.

Ce=coefiicient of expansion of protractor member 2 It, 2 I I.

Cz=coefiicient of expansion of tie member 2 I6.

gar ens The three embodiments 'd's'c'l'ibbd ih detail are'i given-by way of illustrationo-f the invention. The

invention provides a'l'iolding' means in the" a rtof mounting glass circles in theodolites which' may move is an axial" direction duringteinperature changes to com ensate for unequal expansions" in the diametricaldi're'ction. Many variations maybe made of the specifi'cembodiments shown Within the scope of the invention. The invention been illustrated with respect to the-horizontal circle of ying instrument or theodoli't'e which is mounted for" rotationabout a v'r'ertical axis. It may also be used in" connection with other raduate-u circles" mounted for rotationabout' any axis including the vertical circle of asurveying instrument or theo'dol ite which is mounted for rotation ab'outa' horizontalax-is;

What is claimed is:

1 In a theod'olite' having a telescope mounted" for-rotationabout an axis, a'pi-otractor"membe1' of substantially uniform coelfi'cie'n'tof expansion provided with graduations for indicating the:

angularpositionof said telescope on the axis; at

supporting member for said I protractoi member, havinga different coellicient of expansion-than said protractor member and which is mounted" alltempera-tures and means for reading said protractor member to determine the angular position of said-telescope on the axis.

2L In a theodolite'having atelescope mounted for rotation about-an axis; .a protractor member of substantially uniform coeliicient of expansionand including a vitreous transparent circle with graduations for indicating the angular position of said telescope on the axis, a support for said protractoimember having a-difierent coefficient of expansion than: said vitreous transparent circle' and which is mounted for rotationabout the axis, a holding member for said protractor-memher having substantially thesame coefiicientof expansion as said support which expands and contracts in a radial direction at a diiierent rate for any temperature variation than said protractor member, said holding member and said support being held together so that said holding member may not move with respect to said support in any but the axial direction, aninclinedc surface on one of said members positively en gaging the other member with substantially uniform pressure' regardless of' the temperature" variation and retaining said protrac'tor member to hold saidvitreoustransparentcircle"positively" and without strain in centered position on the axis for all temperatures and means for reading:

said protractor member-to determinethe angular position of said telescope on the axis.

3, In a theodolite having a telescope mounted forgrotationeabout an-axis, a protracton memberofsubstantiallyuniform coeffi'cient of expansion and including a vitreous transparent circle provided with' g raduations for'indicating the angular position of the telescope on the axis, a support for said protractor member having a different coefficient of expansion than said vitreous transparent circle'and'which is mounted for rotation about the axis, a holding. member having sub-'- stantially the samecoefiicient of expahsion as said-supportsecured to said support; a surfaceinclined to the axis' of rotation on one of said members engaging the other member, said surface beingso inclined to the axis so: that during temperature changes the difference in axial-ex;

ii pansion between saidholdingmember and said protractor member-causes axial movement be tween the portion of said holding member which engages said protractor member and the en-- gaging portion of'said protractor member to'compensateunequal radial expansion of said pro-- tractor member and said holding member thereby ho'ldingesaid-vitreous transparent circle positively and without strain in centered position onthe axis for all temperatures and means for reading said protractor member to determine the angular position of said telescope on the axis. 4. In a theodolite having a telescope mounted for'rotatio'n' about anaxis a" protractormember of substantially uniform coefficient of expansion and including a vitreous transparent circle provided with graduations'for indicating the angular position of said telescope on the axis, a support for said protractor member having a diiferent coeliicient'of expansion than said vitreous transparent circle and which is mounted for rotation about the axis, a holding member having sub stantially the samecoefficient' of expansion as said support; a surface inclined to the axis of rotation'onone ofsaid members engaging the other member, resilient means urging said holding member in the axial direction and'thereby said surface into engagement with the other member, so that during temperature changes" the portion of said holding member which en'- ga'g'es said protractor member moves axially against the action of said resilient means with respectto the engaging portion of said protractor member to compensate unequal radial expansion of said protracto'r member and said holdingmember thereby holding said vitreous transparent circie' po'sitivelyand without strain in centered position onthe for all temperatures and means for reading said protractor' member to determine the angular position of said telescope on the axis.

5. In" a theodolite having a telescope mounted for rotation about an axis; a vitreous transparent circle provided with graduations for indicating the{angular position of said telescope on'tiie' axis; a protractor member including said vitreous transparent circle anda mount therefor of a material having substantially the same c'oeifi'cient' of expansion as said vitreous transp'are'nt 'ci'rcle so" that=said protract'or member has" asubstantially uniform coeiiicient of expansion, a support for said protractor member having a differentcoelficient of expansion than said" vitreous'transparent circle and which is mounted for rotation'about the axis, a holding member having substantially the same coeficient of expansion as said support, said holding member and said support being held together so that saidholdingmember may move with respect tosaid sup-- port in-the axiaidirectiononly; a surface-inclined; to; the :ax is of. rotatiorron oneof "said members;

engaging the other member in such a manner so that during temperature changes the portion of said holding member which engages said protractor member moves axially with respect to the engaging portion of said protractor member to compensate unequal radial expansion of said protractor member and said holding member thereby holding said vitreous transparent circle positively and without strain in centered position on the axis for all temperatures and means for reading said protractor member to determine the angular position of said telescope on the axis.

6. In a theodolite having a vitreous transparent circle provided with graduations, a protractor member including said vitreous transparent circle and an annular mount therefor having an inner conical surface of a material having substantially the same coefficient of expansion as said vitreous transparent circle so that said protractor member has a substantially uniform coefficient of expansion, a support for said protractor member whereon a bottom surface of said protractor member rests and which has a different coefficient of expansion than said vitreous transparent circle and which is mounted for rotation about an axis, a holding member having substantially the same coeflicient of expansion as said support secured to said support and having an external conical surface engaging the internal conical surface of said annular mount for said vitreous transparent circle, D being the mean diameter of said engaging conical surfaces, d being the axial distance between the plane at which the diameter of said engaging conical surfaces equals the mean diameter and the bottom surface of said protractor member and being the angle which said engaging conical surfaces make with said axis, the equation D tan 9a being substantially satisfied, so that during temperature changes said internal and external surfaces move axially with respect to each other to compensate unequal radial expansion of said protractor member and said holding member thereby holding said vitreous transparent circle positively and without strain in centered position on the axis for all temperatures.

7. In a theodolite having a vitreous transparent circle provided with graduations, a protractor member including said vitreous transparent circle having an inner conical surface, said protractor member having a substantially uniform coefiicient of expansion, a supporting member for said protractor member whereon a bottom surface of said protractor member rests which has a higher coeflicient of expansion than said protractor member and which is mounted for rotation about an axis, a holding member having substantially the same coefficient of expansion as said supporting member, having an external conical surface engaging the internal conical surface of said protractor member and being mounted for axial movement with respect to said supporting member, a tie member restraining the axial movement of said holding member with respect to said supporting member having a higher coefiicient of expansion than said supporting member, the relative dimensions being chosen so that during temperature changes said internal and external conical surfaces move axially with respect to each other to compensate unequal radial expansion of said protractor memi0 ber and said holding member thereby holding said vitreous transparent circle positively and without strain in centered position on the axis for all temperatures.

8. In a theodolite having a vitreous transparent circle provided with graduations, a protractor member including said vitreous transparent circle having an inner conical surface, said protractor'member having a substantially uniform coefficient of expansion Co, a support for said protractor member whereon a bottom surface of said protractor member rests which has a higher coefficient of expansion CB than said protractor and which is mounted for rotation about an axis, a holding member having substantially the same coefiicient of expansion CB as said support, having an external conical surface making an angle 0 with said axis engaging the internal conical surface of said protractor member at a mean diameter D, the distance from the plane at which said engaging conical surfaces have the mean diameter to the bottom surface of the protractor member being 01, said holding member being mounted for axial movement with respect to said support, a tie member having a higher coefficient of expansion Cz than said support restraining the axial movement of said holding member having axially spaced surfaces one of which is fixed with respect to said holding member and the other of which is fixed with respect to said support, the distance between said spaced surfaces being (11, the equation:

being substantially satisfied so that during temperature changes said internal and external conical surfaces move axially with respect to each other to compensate unequal radial expansion of said protractor member and said holding member thereby holding said vitreous transparent circle positively and without strain in centered position on the axis for all temperatures.

9. In a theodolite having a vitreous transparent circle provided with graduations, a protractor member including said vitreous transparent circle and a mount therefor of an iron nickel alloy having substantially the same coefiicient of expansion as said vitreous transparent circle so that said protractor member has a substantially uniform coefiicient of expansion, a support for said protractor member having a diiferent coeficient of expansion than said vitreous transparent circle and which is mounted for rotation about an axis, a holding member having substantially the same coefficient of expansion as said support, said holding member and said support being held together so that said holding member may move with respect to said support in the axial direction only, a surface inclined to the axis of rotation on one of said members engaging the other member in such a manner so that during temperature changes the portion of said holding member which engages said protractor member moves axially with respect to the engaging portion of said protractor member to compensate unequal radial expansion of said protractor member and said holding member thereby holding said vitreous transparent circle positively and without strain in centered position on the axis for all temperatures.

tan 0= GEORGE GEIER.

(References on following page) UNITED F'ISTATES iPATENTS Number Name Date 7 Previdey cs ptt 22,1914 Fouasse V .Dec.\23, 1919 Egy et a1 May 12,1934 Bates Novb 14.. 19.39

Arnold .et a1 Nov. 11,1947

Number 12 FOREIGN PATENTS Country Date Great Britain June 1-7, 1935 Great Britain Feb. Y 19, I940 Great'Britain Sept5lg1944 France Nov. 16,1933

OTHER, REFERENCES Metals Handbook (1939 edition), published-by 10 American Society for :Metals, 7301 Euclid Ave Cleveland, Ohio, pages 465-470, Low Expansion Alloys. 

